Chronic Fetal Anemia Research Articles

Recognising Fetal Compromise in the Cardiograph during the Antenatal Period: Pearls and Pitfalls

There are several national and international guidelines to aid the interpretation of the cardiotocograph (CTG) trace during labour. These guidelines are based on assessing changes in the fetal heart rate (i.e. cardiograph) in response to mechanical and hypoxic stresses during labour secondary to ongoing frequency, duration and strength of uterine contractions (i.e. tocograph). However, during the antenatal period, uterine contractions are absent, and therefore, these intrapartum CTG guidelines cannot be used to reliably identify fetuses at risk of compromise. Computerised analysis of CTG using the Dawes-Redman Criteria could be used to detect fetal compromise. However, clinicians should be aware of the multiple pathways of fetal damage (i.e. inflammation, infection, intrauterine fetal stroke, chronic fetal anaemia, acute feto-maternal haemorrhage and fetal cardiac or neurological disorders) which can cause changes on the CTG trace which may not be recognised by using CTG guidelines.

Role of adenosine signaling in coordinating cardiomyocyte function and coronary vascular growth in chronic fetal anemia.

Fetal anemia causes rapid and profound changes in cardiac structure and function, stimulating proliferation of the cardiac myocytes, expansion of the coronary vascular tree, and impairing early contraction and relaxation. Although hypoxia-inducible factor-1α is sure to play a role, adenosine, a metabolic byproduct that increases coronary flow and growth, is implicated as a major stimulus for these adaptations. We hypothesized that genes involved in myocardial adenosine signaling would be upregulated in chronically anemic fetuses and that calcium-handling genes would be downregulated. After sterile surgical instrumentation under anesthesia, gestationally timed fetal sheep were made anemic by isovolumetric hemorrhage for 1 wk (16% vs. 35% hematocrit). At 87% of gestation, necropsy was performed to collect heart tissue for PCR and immunohistochemical analysis. Anemia increased mRNA expression levels of adenosine receptors ADORA 1, ADORA2A, and ADORA2B in the left and right ventricles (adenosine receptor ADORA3 was unchanged). In both ventricles, anemia also increased expression of ectonucleoside triphosphate diphosphohydrolase 1 and ecto-5'-nucleotidase. The genes for both equilibrative nucleoside transporters 1 and 2 were expressed more abundantly in the anemic right ventricle but were not different in the left ventricle. Neither adenosine deaminase nor adenosine kinase cardiac levels were significantly changed by chronic fetal anemia. Chronic fetal anemia did not significantly change cardiac mRNA expression levels of the voltage-dependent L-type calcium channel, ryanodine receptor 1, sodium-calcium exchanger, sarcoplasmic/endoplasmic reticulum calcium transporting ATPase 2, phospholamban, or cardiac calsequestrin. These data support local metabolic integration of vascular and myocyte function through adenosine signaling in the anemic fetal heart.

Functional adaptations of the coronary microcirculation to anaemia in fetal sheep.

In fetuses, chronic anaemia stimulates cardiac growth; simultaneously, blood flow to the heart muscle itself is increased, and reserve blood flow capacity of the coronary vascular bed is preserved. Here we examined functional adaptations of the capillaries and small blood vessels responsible for delivering oxygen to the anaemic fetal heart muscle using contrast-enhanced echocardiography. We demonstrate that coronary microvascular flux rate doubled in anaemic fetuses compared to control fetuses, both at rest and during maximal flow, suggesting reduced microvascular resistance consistent with capillary widening. Cardiac fractional microvascular blood volume was not greater in anaemic fetuses, suggesting that growth of new microvascular vessels does not contribute to the increased flow per volume of myocardium. These unusual changes in microvascular function during anaemia may indicate novel adaptive strategies in the fetal heart. Fetal anaemia causes cardiac adaptations that have immediate and life-long repercussions on heart function and health. It is known that resting and maximal coronary conductance both increase during chronic fetal anaemia, but the coronary microvascular changes responsible for the adaptive response are unknown. Until recently, technical limitations have prevented quantifying functional capillary-level adaptations in the in vivo fetal heart. Our objective was to characterise functional microvascular adaptations in chronically anaemic fetal sheep. Chronically instrumented fetuses were randomized to a control group (n=11) or were made anaemic by isovolumetric haemorrhage (n=12) for 1week prior to myocardial contrast echocardiography at 85% of gestation. Anaemia augmented cardiac mass by 23% without changing body weight. In anaemic fetuses, microvascular blood flow per volume of myocardium was twice that of control fetuses at rest, during vasodilatory hyperaemia, and during hyperaemia plus increased aortic pressure. The elevated blood flow was attributable almost entirely to an increase in microvascular blood flux rate whereas microvascular blood volumes were not different between groups at baseline, during hyperaemia, or with hyperaemia plus increased aortic pressure. Increased coronary microvascular flux rate in response to chronic fetal anaemia is consistent with expected reductions in capillary resistance from capillary diameter widening detected in earlier histological studies.

Acute and chronic fetal anemia as a result of fetomaternal hemorrhage.

Introduction. Fetomaternal hemorrhage represents a transfer of fetal blood to the maternal circulation. Although many etiologies have been described, most causes of fetomaternal hemorrhage remain unidentified. The differentiation between acute and chronic fetomaternal hemorrhage may be accomplished antenatally and may influence perinatal management. Case. A 36-year-old gravida 6 para 3 presented at 37 and 5/7 completed gestational weeks with ultrasound findings suggestive of chronic fetal anemia such as right ventricular enlargement, diminished cerebral vascular resistance, and elevated middle cerebral artery end-diastolic velocity. On the other hand, signs of acute fetal decompensation such as deterioration of the fetal heart tracing, diminished biophysical score, decreased cord pH, and increased cord base deficit were noted. Following delivery, the neonate's initial hemoglobin was 4.0 g/dL and the maternal KB ratio was 0.015 indicative of a significant fetomaternal hemorrhage. Discussion. One should consider FMH as part of the differential diagnosis for fetal or immediate neonatal anemia. We describe a unique case of FMH that demonstrated both acute and chronic clinical features. It is our hope that this case will assist practitioners in differentiating acute FMH that may require emergent delivery from chronic FMH which may be able to be expectantly managed.

214: Left ventricular Tachykinin 1 gene expression is increased in chronically anemic fetal sheep

increased in chronically anemic fetal sheep Juulia Junno, Juha Rasanen, Jennifer Farwell, Roger Hohimer, Olli Vuolteenaho, Lowell Davis, Sonnet Jonker University of Oulu, Physiology, Oulu, Finland, Oregon Health and Science University, Obstetrics and Gynecology, Portland, OR, Kuopio University Hospital, Obstetrics and Gynecology, Kuopio, Finland, Oulu University Hospital, Obstetrics and Gynecology, Oulu, Finland OBJECTIVE: Chronically anemic fetuses increase cardiac output by 50%. Anemia-induced cardiac remodeling is associated with diminished isovolumic contraction velocity acceleration (IVCVacc) and isovolumic relaxation velocity deceleration (IVRVdec) in the left ventricle indicating reduced ventricular contractility and relaxation. We therefore sought to determine if there were changes in genes that affect ventricular function in chronically anemic fetuses. STUDY DESIGN: 7 fetal sheep with twin gestations had catheters placed surgically and 1 randomly selected twin was made anemic by daily isovolumic hemorrhage for 8 days. At 126 days gestation echocardiographic studies were performed under anesthesia and tissues from the right (RV) and left (LV) ventricles were obtained. Agilent’s 8x15K Sheep Gene Expression array with greater than 2 fold changes were selected for qRT-PCR. RESULTS: Hematocrit was reduced in anemic fetuses as compared to controls 13.1 (2.5) vs 34.9 (5.2)% means (SD) as well as oxygen content 2.3 (0.4) vs 8.4 (1.7) ml/dl. LV and RV IVCVacc and IVRVdec, and MRNA expression/18s are shown below. All the data are presented as means (SD).* p 0.05. CONCLUSION: Neither changes in -adrenergic receptor 1, phospholamban, nor troponin C account for the decrease in left ventricular contractility and relaxation in anemic fetuses. Increased Tachykinin 1 gene expression through substance P and neurokinin A may be important in mediating decreased ionotropy and lusitropy in chronic fetal anemia.

Hemorragia fetomaterna masiva como causa de hidrops en gestación a término. Reporte de caso y revisión de la literatura

Objetivo: la hemorragia fetomaterna masiva es una complicación rara del embarazo, que puede causar anemia fetal severa y muerte fetal intrauterina. Se presenta un caso clínico con el objetivo de hacer una revisión de la fisiopatología del diagnóstico y del tratamientoMateriales y métodos: se presenta el caso clínico de una mujer en la semana 39 de embarazo, remitida al Hospital La Paz de Madrid, centro de referencia de atención materna y perinatal, por signos ecográficos de hidrops y de insuficiencia cardíaca derecha. El registro cardiotocográfico evidenció un patrón sinusoidal. La recién nacida presentó acidosis metabólica y anemia severa. El estudio anatomopatológico de la placenta fue sugestivo de anemia fetal crónica. El test de Kleihauer-Betke evidenció hemorragia fetomaterna de 90-100 ml. Se realizó una búsqueda bibliográfica en las bases de datos Medline vía Pubmed, EMBASE, LILACS y SciELO y la biblioteca Cochrane.Conclusión: el diagnóstico intrauterino es difícil, se debe sospechar cuando una mujer refiere reducción de movimientos fetales y cuando el registro cardiotocográfico muestra un patrón sinusoidal. En general, el estudio ecográfico es anodino, el Doppler de la arteria cerebral media puede ayudar en la identificación de los casos de anemia fetal, donde se evidencia un aumento del pico sistólico. Es importante la identificación precoz de los casos afectados para empezar un tratamiento sintomático de la anemia.

Transfusion Effects on Cardiomyocyte Growth and Proliferation in Fetal Sheep After Chronic Anemia

Chronic fetal anemia results in significant cardiac remodeling. The capacity to reverse these effects is unknown. We examined the effects of transfusion on cardiomyocyte adaptations after chronic anemia in fetal sheep subjected to daily hemorrhage beginning at 109-d GA (term ∼145 d). After 10 d of anemia, one group was killed for comparison with age-matched controls. A separate group of anemic fetuses was transfused with red blood cells at 119-d GA for comparison with controls at 129-d GA. Anemia significantly increased the heart-to-body weight ratio, an effect partially ameliorated after transfusion. Cardiomyocyte dimensions were similar among all groups, suggesting an absence of hypertrophy. The percentages of mono- and binucleated cardiomyocytes were similar between groups at 119-d GA, although the percentage of binucleated cells was significantly less in transfused fetuses compared with controls at 129-d GA. Protein levels of mitogen-activated protein kinases and protein kinase B were similar between controls and their respective intervention groups, except for a significant increase in phosphorylated c-Jun N-terminal kinase 1/2 in transfused fetuses. Thus, cardiomyocyte proliferation but not hypertrophy contributes to cardiac enlargement during fetal anemia. Transfusion results in slowing but not cessation of cardiac growth after anemia.

Regional Myocardial Function and Response to Acute Afterload Increase in Chronically Anemic Fetal Sheep: Evaluation by Two-Dimensional Strain Echocardiography

We hypothesized that in chronic fetal anemia, remodeling of the myocardium is related to abnormalities in regional wall motion and acutely increased afterload further disturbs myocardial strain. Chronic anemia was induced in one fetus of each of seven sheep twin pregnancies. The fetuses were studied by two-dimensional (2-D) strain echocardiography at baseline and during increased afterload via angiotensin II (AT II) infusion. At baseline, the peak systolic longitudinal, radial and circumferential strains in the left ventricular lateral wall in anemic fetuses were lower than those in the controls (all p < 0.05). During AT II, the circumferential strain of right ventricular free wall decreased significantly both in the control and anemic fetuses. Left ventricular free wall systolic strains were not affected by AT II. Fetal myocardial remodeling in chronic anemia decreases left ventricular systolic free wall strains. The myocardial adaptation does not change ventricular responses to acutely increased afterload. (E-mail: sahnd@ohsu.edu)

Cardiomyocyte enlargement, proliferation and maturation during chronic fetal anaemia in sheep

Chronic anaemia increases the workload of the growing fetal heart, leading to cardiac enlargement. To determine which cellular process increases cardiac mass, we measured cardiomyocyte sizes, binucleation as an index of terminal differentiation, and tissue volume fractions in hearts from control and anaemic fetal sheep. Fourteen chronically catheterized fetal sheep at 129 days gestation had blood withdrawn for 9 days to cause severe anaemia; 14 control fetuses were of similar age. At postmortem examination, hearts were either enzymatically dissociated or fixed for morphometric analysis. Daily isovolumetric haemorrhage reduced fetal haematocrit from a baseline value of 35% to 15% on the final day (P < 0.001). At the study conclusion, anaemic fetuses had lower arterial pressures than control fetuses (P < 0.05). Heart weights were increased by 39% in anaemic fetuses compared with control hearts (P < 0.0001), although the groups had similar body weights; the heart weight difference was not due to increased ventricular wall water content or disproportionate non-myocyte tissue expansion. Cardiomyocytes from anaemic fetuses tended to be larger than those of control fetuses. There were no statistically significant differences between groups in the cardiomyocyte cell cycle activity. The degree of terminal differentiation was greater in the right ventricle of anaemic compared with control fetuses by 8% (P < 0.05). Anaemia substantially increased heart weight in fetal sheep. The volume proportions of connective and vascular tissue were unchanged. Cardiomyocyte mass expanded by a balanced combination of cellular enlargement, increased terminal differentiation and accelerated proliferation.

66: Chronic fetal anemia increased cardiac wall thickness and preserved right ventricular function during acutely increased afterload

66: Chronic fetal anemia increased cardiac wall thickness and preserved right ventricular function during acutely increased afterload

Effect of fetal anaemia on myocardial ischaemia–reperfusion injury and coronary vasoreactivity in adult sheep

We investigated whether chronic fetal anaemia affects myocardial infarct in adulthood and elicits functional modifications in adult coronary vasoreactivity. Seven-month-old sheep that were made anaemic in utero and transfused to normal haematocrit before birth were studied. Infarct size was determined by tetrazolium after 1-h ischaemia (occlusion of the mid of left anterior descending artery) and 2-h reperfusion. The dose-response to vasoconstrictors and vasodilators was assessed in small resistance coronary arteries. There were no significant differences between the animals previously subjected to in utero anaemia and the control animals regarding the percentage infarct size and the area-at-risk to the left ventricle. The ventricular function (dP/dt) was preserved. The percentage infarct size of the area-at-risk (70.7 +/- 3.5%) was larger than that in the controls (49.8 +/- 4.5%) (P = 0.006). The vascular responses were not altered. Endothelium-dependent relaxation to bradykinin (96.0 +/- 2.6% vs. 98.8 +/- 1.0%) was not affected by PGI(2) inhibitor (94.6 +/- 2.6% vs. 98.5 +/- 1.0%) but significantly reduced by the inhibition of nitric oxide (NO) in both anaemic (P < 0.05) and control (P < 0.001) groups with a significant right shift of EC(50) (P < 0.01). The non-NO-non-PGI(2)-mediated relaxation was slightly potentiated in anaemic animals. Exposing fetal sheep to in utero anaemia in late gestation for 3 weeks may increase the susceptibility of adult hearts to ischaemia-reperfusion injury without major alterations in coronary vasomotor responsiveness. The impact of in utero anaemia at earlier period of pregnancy and on the earlier or later life of the adult is yet to be further investigated.

Fetal Programming of Cardiac Function and Disease

Fetal programming describes long-term adaptive changes that an organism undergoes in response to an intrauterine insult. This term was coined to describe the increased incidence of adult disease, such as cardiovascular disease, seen among populations that suffered an intrauterine insult. While changes induced by such an insult may be initially beneficial, they can have deleterious long-term effects. Cardiac programming effects can be induced by maternal diet alterations, fetal exposure to increased levels of corticosteroids, chronic fetal hypoxia and anemia, and maternal use of nicotine or cocaine. These stimuli result in a variety of changes in cardiac function and gene expression, many of which persist into adulthood. A possible mediator of these changes is an alteration in the DNA methylation pattern of the cardiomyocytes. This review gives an overview of the changes that have been observed in the heart in response to various programming stimuli and potential programming mechanisms.

Prenatal anemia and adult coronary endothelial function

We previously demonstrated cardiovascular adaptations to chronic fetal anemia with persistence into adult life. We further investigated whether the increase in coronary blood flow and in coronary conductance is attributable to augmented coronary endothelial function. Right coronary small arteries (diameter 200–450 μm) from 7-month old adult sheep with in-utero anemia were studied. The vasorelaxant response to bradykinin (BK, −10~−6.5 logM) was determined with the role of PGI2, nitric oxide (NO) and non-NO-non-PGI2 (NNONPG)-mechanism explored. BK-induced, endothelium-dependent relaxation did not differ between the adult experienced in-utero anemia (96.0±2.6%) and their non-anemic siblings (control, 98.8±1.0%). Indomethacin did not affect the response to BK. Inhibition of NO markedly reduced the relaxation (repeated measures) in both anemic (p<0.05) and control groups (p<0.001) with EC50 right shifted (anemia: −8.70±0.11 vs. −8.14±0.18 logM, p<0.05; control: −8.49±0.12 vs. −7.86±0.13 logM, p<0.01). The NNONPG-mechanism contributed more in anemic animals (p=0.022, two-way ANOVA). Thus, both NO and NNONPG-mechanisms, but unlikely the PGI2-mechanism are involved in sheep coronary vasodilatation. The NNONPG-mechanism is slightly upregulated by in-utero anemia although the endothelial function, as a whole, remains unchanged.

Myocardial vascular and metabolic adaptations in chronically anemic fetal sheep

Little is known about the vascular and metabolic adaptations that take place in the fetal heart to maintain cardiac function in response to increased load. Chronic fetal anemia has previously been shown to result in increased ventricular mass, increased myocardial vascularization, and increased myocardial expression of hypoxia-inducible factor-1 (HIF-1) and vascular endothelial growth factor (VEGF). We therefore sought to determine whether chronic fetal anemia induces expression of HIF-1-regulated angiogenic factors and glycolytic enzymes in the fetal myocardium. Anemia was produced in chronically instrumented fetal sheep by daily isovolemic hemorrhage (80-100 ml) for either 3 (n = 4) or 7 days (n = 11) beginning at 134 days of gestation (term 145 days). Catheterized, nonbled twins served as controls. Isovolemic hemorrhage over 7 days resulted in decreased fetal hematocrit (37 +/- 1 to 20 +/- 1%) and arterial oxygen content (6.5 +/- 0.4 to 2.8 +/- 0.2 ml O2/dl). Myocardial blood flow and vascularization were significantly increased after 7 days of anemia. Myocardial HIF-1 protein expression and VEGF (left ventricular), VEGF receptor-1 (right ventricular), and VEGF receptor-2 (right ventricular, left ventricular) mRNA levels were elevated (P < 0.05) in 7-day anemic compared with control animals. Myocardial expressions of the glycolytic enzymes aldolase, lactate dehydrogenase A, phosphofructokinase (liver), and phosphoglycerol kinase were also significantly elevated after 7 days of anemia. Despite the absence of a significant increase in myocardial HIF-1alpha protein in 3-day anemic fetuses, expressions of VEGF, VEGF receptor-1, and the glycolytic enzymes were greater in 3-day compared with 7-day anemic animals. These data suggest that HIF-1 likely participates in the fetal myocardial response to anemia by coordinating an increase in gene expressions that promote capillary growth and anaerobic metabolism. However, factors other than HIF-1 also appear important in the regulation of these genes. We speculate that the return of mRNA levels of angiogenic and glycolytic enzymes toward control levels in the 7-day anemic fetus is explained by a significantly increased resting myocardial blood flow, resulting from coronary vascular growth and increased coronary conductance, and a return to a state of adequate oxygen and nutrient delivery, obviating the need for enhanced transcription of genes encoding angiogenic and glycolytic enzymes.

The effects of anaemia as a programming agent in the fetal heart

The intrauterine environment plays a powerful role in determining the life-long risk of cardiovascular disease. A number of stressors are well known to affect the development of the cardiovascular system in utero including over/under maternal nutrition, excess glucocorticoid and chronic hypoxia. Chronic fetal anaemia in sheep is a complex stressor that alters cardiac loading conditions, causes hypoxic stress and stimulates large changes in flow to specific tissues, including large increases in resting coronary blood flow and conductance. Decreased viscosity can account for approximately half of the increased flow. It appears that immature hearts are 'plastic' in that increases in coronary conductance with fetal anaemia persist into adulthood even if the anaemia is corrected before birth. These large changes in conductance are possible only through extensive remodelling of the coronary tree. Adult hearts that were once anaemic in utero are more resistant to hypoxic stress as adults but it is not known whether such an adaptation would be deleterious in later life. These studies indicate the need for investigation into the basic mechanisms of coronary tree remodelling in the immature myocardium. New information on these mechanisms is likely to lead to better prevention of and therapies for adult-onset coronary disease.

Fetal anemia leads to augmented contractile response to hypoxic stress in adulthood.

In response to chronic fetal anemia, coronary blood flow, maximal coronary conductance, and coronary reserve increase. We sought to determine whether chronic fetal anemia alters left ventricular (LV) function in adulthood. We studied adult sheep that had been made anemic for 20 days in utero by phlebotomy. They were transfused just before birth. At 7 mo of age, LV function was measured by pressure-volume loops at rest and during hypoxic stress. The in utero anemia group (n = 8) did not differ from controls (n = 5) with respect to hematocrit, heart and body weight, or baseline hemodynamic parameters. However, the effect of hypoxia (relative to baseline) on multiple indexes of systolic function was different between the two groups. End-systolic elastance increased in the in utero anemia group (baseline to hypoxia) by 4.15 +/- 3.47 mmHg/ml (mean +/- SD) but changed little in controls (0.24 +/- 0.45), which shows that the response to hypoxia was significantly different (P < 0.01) between groups. Similarly, the maximum derivative of LV pressure with respect to time increased in the in utero anemia group (486 +/- 340 mmHg/s,) but on average fell in the controls (-503 +/- 211 mmHg/s) with the response again being significantly different (P < 0.03). We conclude that in sheep, perinatal anemia can alter cardiac responses to hypoxic stress in the adult long after restoration of normocythemia.

Myocardial blood flow and coronary reserve in chronically anemic fetal lambs.

Chronic fetal anemia produces large compensatory increases in coronary blood flow in the near-term fetal lamb. To determine if increased coronary flow in anemic fetuses is associated with decreased coronary flow reserve or, alternatively, an increase in coronary conductance, we measured maximal coronary artery conductance during adenosine infusion before and during anemia. Isovolemic hemorrhage over 7 days reduced hematocrit from 30.6 +/- 2. 7 to 15.8 +/- 2.4% (P < 0.02) and the oxygen content from 7.3 +/- 1. 4 to 2.6 +/- 0.4 ml/dl (P < 0.001). Coronary blood flow increased from control (202 +/- 60) to 664 +/- 208 ml. min(-1). 100 g(-1) with adenosine to 726 +/- 169 ml. min(-1). 100 g(-1) during anemia and to 1,162 +/- 250 ml. min(-1). 100 g(-1) (left ventricle) during anemia with adenosine infusion (all P < 0.001). Coronary conductance, determined during maximal vasodilation, was 18.2 +/- 7.7 before and 32.8 +/- 11.9 ml. min(-1). 100 g(-1). mmHg(-1) during anemia (P < 0. 001). Coronary reserve, the difference between resting and maximal myocardial blood flow interpolated at 40 mmHg, was unchanged in control and anemic fetuses (368 +/- 142 and 372 +/- 201 ml/min). Because hematocrit affects viscosity, anemic fetuses were transfused with blood to acutely increase the hematocrit back to control, and conductance was remeasured. Coronary blood flow decreased 57.3 +/- 18.9% but was still 42.6 +/- 18.9% greater than control. We conclude that in chronically anemic fetal sheep coronary conductance is increased and coronary reserve is maintained, and this is attributed in part to angiogenesis as well as changes in viscosity.

Cardiac hypertrophy in chronically anemic fetal sheep: Increased vascularization is associated with increased myocardial expression of vascular endothelial growth factor and hypoxia-inducible factor 1

OBJECTIVE: Our purpose was to determine whether the increase in fetal cardiac mass and cardiac output in chronic anemia is accompanied by changes in capillary density or size or changes in levels of vascular endothelial growth factor and hypoxia-inducible factor 1, a basic helix-loop-helix transcription factor that has previously been shown to activate vascular endothelial growth factor gene transcription when cultured cells are subjected to hypoxia. STUDY DESIGN: Anemia was induced in near-term ovine fetuses by daily isovolemic hemorrhage. In five fetuses the heart was arrested in diastole, isolated, and fixed at physiologic pressures with adenosine-paraformaldehyde, and morphometric measurements of capillaries were made. In six fetuses cardiac expression of vascular endothelial growth factor and hypoxia-inducible factor 1 protein was detected by Western analysis and vascular endothelial growth factor messenger ribonucleic acid by Northern blot analysis. Eleven age-matched fetuses served as controls. RESULTS: The anemic fetuses compared with controls had a lower hematocrit (14.8% ± 0.7% vs 35.3% ± 1.5%) and a greater heart-to-body weight ratio (10.5 ± 1.1 vs 7.7 ± 0.5 gm/kg). The minimal capillary diameter was increased and the intercapillary distance was decreased in both right and left ventricles of anemic fetuses compared with controls. Vascular endothelial growth factor protein was increased 4.5-fold, vascular endothelial growth factor messenger ribonucleic acid 3.2-fold, and hypoxia-inducible factor 1α protein 3.8-fold in ventricular tissue from anemic fetuses. CONCLUSIONS: In chronic fetal anemia cardiac hypertrophy is accompanied by anatomic changes in myocardial capillary morphometry along with induction of hypoxia-inducible factor 1 and vascular endothelial growth factor. These results provide evidence for a pathway by which anemia-hypoxia may stimulate myocardial vascularization. (Am J Obstet Gynecol 1998;178:527-34.)

Changes in left thoracic duct lymph flow during progressive anemia in the ovine fetus

OBJECTIVE: The purpose of this study was to evaluate the extent to which increased lymph flow can return fluid and protein to the circulation in the chronically anemic fetus. STUDY DESIGN: Thoracic duct lymph flow rate over a range of outflow pressures was measured in 8 near-term fetal sheep 4 to 5 days after surgery and daily thereafter for 5 days. After each day's study 60 to 150 ml of blood was withdrawn at a rate of 1 ml per minute. Regression analysis was used to establish the lymph flow function curve. Lymph and plasma protein concentrations and lymph flow rate were compared by analysis of variance for repeated measures. RESULTS: As the hematocrit was reduced from 34.6% ± 1.3% (mean ± SE) to 14.4% ± 1.0%, thoracic duct lymph flow increased from 0.12 ± 0.01 to 0.28 ± 0.02 ml/min/kg. Plasma total protein concentration did not change, lymph protein concentration fell (2.6 ± 0.1 to 2.4 ± 0.1 gm/dl), and the difference between plasma and lymph protein concentrations increased (1.04 ± 0.05 to 1.34 ± 0.10 gm/dl). Protein returned to the circulation increased from 11.5 ± 0.3 to 23.7 ± 1.5 mg per minute. Central venous pressure did not change and remained less than the breakpoint pressure. Although the plateau lymph flow rate increased, neither the breakpoint or stopflow pressures of the lymph flow function curve were altered. CONCLUSIONS: Fetal lymph flow and thereby capillary filtration increased progressively as anemia became more severe. The increase in lymph flow did not appear to be limited by outflow pressure. By returning protein to the circulation, an increase in thoracic duct lymph flow helped to limit expansion of extravascular fluid volume during chronic fetal anemia. (AM J OBSTET GYNECOL 1996;174:1469-76.)

Right ventricular function in chronically anemic fetal lambs

OBJECTIVE: Our purpose was to determine whether the increase in extravascular fluid in chronic fetal anemia occurs either because of heart failure or despite successful cardiac adaptation. STUDY DESIGN: Right ventricular function curves were obtained in five ovine fetuses at the start, midpoint, and end of 5 to 8 days of anemia induced by isovolemic daily hemorrhage. Least-squares fit of the ascending and plateau lines of stroke volume versus right atrial pressure were used to establish breakpoints (intersection of the ascending and plateau lines), which were compared by analysis of variance for repeated measures. Myocardial blood flow was measured by microspheres. RESULTS: Carotid arterial oxygen content was reduced from 7.0 ± 0.3 to 2.1 ± 0.1 ml/dl and the hematocrit from 29% ± 1.8% to 13% ± 0.6%. Breakpoint analysis of function curves showed that although right atrial pressure remained unchanged (3.4 ± 0.7 and 3.6 ± 0.6 mm Hg) stroke volume increased from 1.03 ± 0.14 to 1.62 ± 0.25 ml/kg. Both right and left ventricular coronary blood flow were increased, 1351 ± 313 and 1166 ± 264 ml/min per 100 gm. Excess fluid was present in the abdomen and chest of most animals at autopsy. CONCLUSION: Tissue edema during severe anemia occurs despite normal right atrial pressure, increased stroke volume, and markedly increased coronary blood flow, markers of successful cardiac adaptation. (A M J O BSTET G YNECOL 1996;174:1289-94.)